The present Invention relates to a harmonic drive according to the preamble of the main claim.
It is known from the type forming pre-publication U.S. Pat. No. 5,370,011 that on the one side of the harmonic drive there is a drive motor and on the other side there is disposed the drive for the ball thread spindle disposed axially opposite to the drive motor, wherein the ball thread spindle extends from here coaxially from the harmonic drive. A thin bore hole runs coaxially through the drive motor and the harmonic drive up to the interior of the spindle, wherein the cross-section of the thin bore hole is filled essentially with the rod axially adjustable and stationery supported at the motor casing, wherein the rod carries a sensor by way of which the momentary axial position of the spindle can be determined relative to the motor casing. Thus the spindle is disposed beyond the drive motor, the spindle does not run through the drive motor itself; and also no other function element or construction element can extend centrally through the drive motor because of the presence of the sensor rod.
The function of this wave gear, known also as harmonic drive or ring belt transmission as a very heavily reducing, self locking system with the power take off rotating coaxially to the drive shaft, rests on the fact that a rotating so-called wave generator radially deforms circulatingly an inside wheel tire and thereby presses on circulatingly and locally the outer jacket face of the inside wheel tire toward the outside against the hollow cylindrical inner jacket face of slightly larger circumference of a stationary, dimensionally stable support ring. Consequently the inside wheel itself or the wheel tire rotatably supported on the inside wheel rolls in the support ring force matchingly over friction faces or shape matchingly over gear splines, where in the wheel or, respectively the tire of the wheel rotates slow or as compared with the motor driven drive core of the wave generator depending on the measure of the difference in circumference. This rotary motion strongly decelerated relative to the drive is preferably transferred through the outer jacket face or, respectively the outer splines of the wheel tire onto the inner jacket face or, respectively, onto the inner splines of a further hollow cylindrical outer ring, of the power take offering disposed concentrically to the support ring, however not stationary disposed but rotatable relative to the hollow cylindrical outer ring. According to the kind forming contribution xe2x80x9cGenial einfachxe2x80x9d of H. Kirn (KEM Antriebstechnik Heft 11, 1996) a cam shaped non-round (oval in axial cross section) drive core is rotated as a wave generator concentrically in the hub of the radially deformable inside wheel. Dimensionally stable spokes operate as radially oriented tappets between the hub circulatingly radially deformed by the drive core and the outer toothed tire of this inside wheel also radially deformable and in fact that the outer splines corresponding to their circulating radial deformation stands in engagement with the inner splines of the support ring in each case only over the limited arcuate piece just rolling off. This harmonic drive is based on its strong reduction and self locking particularly suitable for sensitive and good reproduceable, mechanically stable and manually performable adjustment tasks and setting tasks. A motor drive of such a wave generator usually is performed through a high-speed and therefore cost favorably available low voltage D.C. motor connected coaxially to the drive core, wherein the rotation of the low voltage D.C. motor thus is reduced to a very much slower of a correspondingly larger torque at the power take off shaft. Such motor gear combination is employed in particular in electromechanical, rotary operating adjustment devices in a motor vehicle. If the application requires that the output motion is linear then usually such a motor drive combination is connected to a further transmission for transferring the output rotary motion into a translation motion, wherein frequently the axis of the harmonic drive has to be disposed orthogonal and perpendicular to the axis of the linear drive based on kinematic reasons. For this purpose in particular the kind of construction is known in the drive technology and in the transmission technology, which kind of construction carries a nut on an external extension of the motor shaft furnished with an outer thread, wherein the nut is shifted in longitudinal direction based on the shaft rotation, since the nut is mechanically arrested against a co-rotation. An eccentrically supported swivel lever on this nut is engaged usually with a swivel lever orthogonal and perpendicular disposed to the shaft, wherein the swivel lever transfers the linear motion of the sliding nut as a swivel motion onto the place of operation, which is additionally disadvantageous relative to the overall degree of effectiveness as well as to the space requirements.
The invention is based on the technical problem to further develop the harmonic drive by maintaining the apparatus oriented and application oriented advantages in the direction that further application possibilities, which could not yet be realized up to now based on the construction, in particular also in connection with an equipping as a gear motor, are opened up and are preferably placed constructively into the harmonic drive itself.
The solution of this task characterized in the main claim is designated as a hollow shaft drive based on the large inner diameter in comparison with the ratio to the diameter of the apparatus of a channel extending through the harmonic drive concentrically. This is associated with the advantage to be able to place for example supply lines or construction elements through the center of the transmission. The consideration that the non-round drive core of the harmonic drive, which non-round drive core leads to the described rolling off of the flexible sleeve collar (flex splines) in the support ring, as well as the motor shaft rotating the support ring in a motor drive combination, even then can be realized with sufficient stiffness against torsion, if a tubular construction is performed, which construction determines the passage channel, was a starting point for this solution.
Now electrical or hydraulic supply lines can run concentrically through the harmonic drive, which allows for a preassembled and space saving gear incorporation. Also the harmonic drive can be carried on a stationary passing through pipe conduit spatially fixed in the kind of a sleeve in order to for example set a fluid throttle of the kind of an iris diaphragm in this pipe conduit by immediate attack of the swivelable gear power take off ring at a diaphragm lever projecting radially from the pipe conduit; or a movably supported pin for switching tasks and signal tasks movably supported is running coaxially through the spatially fixed mounted harmonic drive or possibly even in the drive itself, wherein the movably supported pin is adjusted by the power take off ring by rotation or (through a thread engagement) through axial shifting.
An axial power take off with a spindle shaped threaded rod is present in the latter case, wherein the threaded rod is received axially shiftable in the channel of the hollow transmission. This threaded rod mechanically secured against rotation protrudes from the harmonic drive more or less, namely according to the measure of rotation of the power take off ring, wherein the threaded rod is shape matching in engagement with the bearing tappet in the shape of a shaft end inner thread.
This further development of the solution according to the present invention is associated with the advantage to obtain immediately at the output of the harmonic drive a linear output motion without particular apparative additional equipment and therefore both space saving as well as low loss, that is the linear motion of a (threaded) rod relative to the casing of the transmission. The transfer of the motion from the rotation into translation is immediately placed into a wave generator and is thus at the same time integratable into a transmission motor without a requirement of having to substantially increase the radial dimensions of the harmonic drive for this purpose. For example processing tools or work tables can be precisely positioned or sliders or the like can be directly linearly set without an intermediate positioning of worm gears. The transmission motor can here be installed spatially fixed and the rod can move outward and inward; or the rod is for example installed spatially fixed horizontally or vertically and the motor transmission unit rides along this gear rack. The hollow transmission equipped in this manner delivers thus immediately a pre-given translational set value defined through the rotation speed of the power take off ring and therewith of the motor driven wave generator, if the power take off ring of the hollow transmission axially shifts a threaded rod extending otherwise freely and coaxially through a central longitudinal bore hole in the harmonic drive and engaged with the power take off ring, through the rotary motion of the inner thread of the power take off ring, since the threaded rod is secured fixed to the casing against rotation.
An axially short ring disk concentrically rotating around the channel axis can particularly advantageously serve as carrier of at least two eccentric, axially parallel oriented pins as a wave generator instead of a thick walled tubular non-round drive core, wherein an axially wide radially flexible sleeve collar of the kind of a broad toothed belt runs over the pins (and thus axially shifted relative to the ring disk), wherein the flexible sleeve collar circulated with the pin is locally pressed into support rings and power take off rings surrounding the ring disk with its pins and disposed coaxially next to each other in the inner periphery.
An electro-motor drive for this hollow harmonic drive can be disposed externally and can be for example connected to the transmission on the input side through a gear wheel or a worm drive. In the case of a drive side belt drive, the support ring for the circulating pin can serve at the same time as a pulley or, respectively, as a toothed beltxe2x80x94crown gear. However a harmonic drive motor can be more space saving and simpler pre-assembled if the drive of the motor is according to the present invention integrated into the transmission by having the rotor of the motor, which then is furnished on the front side with the support ring for the circulating press on pins, exhibits the shape of a thick-walled hollow cylinder in a ring shaped stator casing.